A Conceptual Model of the Thermal-Spike Mechanism in Graphite/Epoxy Laminates

The influence of a thermal spike on a moisture-saturated graphite/epoxy composite was studied in detail. A single thermal spike from 25 to 132°C was found to produce damage, as evidenced by a significant increase in the level of moisture saturation in the composite. Approximately half of this increase remained after a vacuum-anneal at 150°C for seven days, suggesting the presence of an irreversible damage component. Subsequent thermal spikes created less and less additional moisture absorption, with the cumulative effect being a maximum or limiting moisture capacity of the composite. These observations are explained in terms of a model previously developed to explain the reverse thermal effect of moisture absorption in epoxy and epoxy-matrix composites. This model, based on the inverse temperature dependence of free volume, improves our understanding of thermal-spike effects in graphite/epoxy composites.